1. Field of the Invention
The present invention relates to a method of folding a continuous web of a thermoplastic film material incorporating complementary interengagable profiled fastener elements, and aligning and interengaging the complementary fastener elements. Moreover, the invention relates to a device over which the web of thermoplastic film material is folded, with the device possessing structure for superimposing and aligning the fastener elements and interengaging the fastener elements which are adapted to be utilized in the production of reclosable plastic bags.
Basically, plastic bags which are produced from an extruded thermoplastic film web material, and which bags incorporate resealable closures, such as interengagable fastener elements forming such closures to provide hermetically sealed bags which, subsequent to being opened by separating the interengaged fastener elements, are then reclosable by again engaging the fastener elements, are widely known in the art, and have gained widespread consumer acceptance.
Thus, an extensive variety of products can be readily packaged and stored under widely ranging temperature conditions in such plastic bags, ranging from food items which are adapted to be frozen and/or stored for lengthy periods of times, to hardware, soft goods, and sundry types of materials in either a fluid, solid, or granular-pulverulent state.
Generally, such plastic bags are formed from continuous webs of extruded thermoplastic materials in which complementary fastener elements are integrally coextruded with or attached to the film, with the film then being folded in order to align the fastener elements in a superimposed relationship and with the elements thereafter being interengaged. Subsequently, lateral seals extending transverse of the direction of advance or machine direction of the film web are imparted at predetermined intervals to the folded film, and the film is cut into individual sections, or weakening lines are formed in the regions of such lateral seals in order to form the folded web into individual thermoplastic bags which are either separated or attached to each other along the weakening lines, which may be either perforations, serrations, slits, or score lines in the film.
A major problem which is encountered in the folding of such thermoplastic film material possessing complementary profiled fastener elements for the formation of plastic bags resides in implementing the precise aligning of the fastener elements during the advance of the web at the relatively high production speeds which are necessary for an economical manufacture of such bags.
In order to achieve a maximum production rate for such reclosable thermoplastic bags which are formed from a folded continuous web of a thermoplastic film incorporating complementary interengagable and repeatedly openable fastener elements, it is essential that during the folding of the film web there is effected the precisely aligned superposition between the components of the complementary fastener elements, so as to enable them to be interengaged through the application of external pressure to the film web as the latter is advanced in the machine direction.
2. Discussion of the Prior Art
At this time, the needs of industry in developing methods and devices for aligning and interengaging continuous fastener elements formed on extruded thermoplastic film web material, such as for plastic bags, have not been fully addressed in the technology relating to the high speed formation of reclosable plastic bags constituted of thermoplastic film material.
Thus, Ausnit U.S. Pat. No. 4,196,030 discloses a method for producing extruded thermoplastic bags, wherein a relatively complex manufacturing procedure is employed for folding the thermoplastic film and interengaging male and female profiled fastener elements which form reclosable closures for the film bags, such elements being integral protuberances formed on the film web surface during extrusion of the film.
Zygan, et al. U.S. Pat. No. 3,240,412 discloses an arrangement for handling tensioned webs of foil possessing flanged edges, in which the flanged edges are passed through a clamping device providing a gap sufficiently wide to allow the foil or web to pass therethrough while maintaining the flanged structure on the web in a clamped relationship to allow for appropriate tensioning of the foil web.
Hawley U.S. Pat. No. 3,579,747 discloses a plastic film sheeting having stripping of profiled male and female fastener elements molded along the longitudinal edges thereof. The fastener elements are adapted to be interengaged through the action of an aligning slide fastener block through the openings of which the male and female fastener members are aligned and thereafter interengaged to form a closed fastener arrangement.
Sanborn, Jr. U.S. Pat. No. 4,240,241 discloses a method and apparatus for producing a reclosable package, such as a package constituted of a thermoplastic material in which pressure is applied to cause the interengagement of profiled fastener elements formed on plastic film or package structure.
However, none of the prior art disclosures relate to the folding of thermoplastic film webs in a predetermined manner to align profiled fastener elements formed thereon as the film is conducted at a high rate of speed over a folding apparatus which will align the fastener elements for interengagement thereof.
In essence, the current state of the technology does not make any adequate provision for properly aligning the complementary components of a zipper or continuous profiled fastener elements formed on a thermoplastic film web material which, in particular, is adapted for the production of plastic bags having reclosable openings formed by the fastener elements.